Algebra.Com's Answer #662374 by ikleyn(52817)![\"\"](\"/images/stars/stars-13.gif\")  
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document.write( "A boat travels 80 km downstream in 2.5 hours. It travels 50 km upstream in the same length of time.
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document.write( "what is the speed of the boat in still water and of the current?
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document.write( "For the trip downstream, your first equation is \r\n" );
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document.write( " = u + v, or \r\n" );
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document.write( "32 = u + v. (1)\r\n" );
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document.write( "The term in the left side is the speed of the boat (relative to the bank of the river) on the trip downstream with the river current.\r\n" );
document.write( "Here u is the boat speed in still water and v is the current speed.\r\n" );
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document.write( "For the upstream trip, your second equation is \r\n" );
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document.write( " = u - v, or \r\n" );
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document.write( "20 = u - v. (2)\r\n" );
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document.write( "The term in the left side is the speed of the boat (relative to the bank of the river) on the trip upstream against the river current.\r\n" );
document.write( "Again, here u is the boat speed in the still water and v is the current speed.\r\n" );
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document.write( "Rewrite the equations (1) and (2) in this way:\r\n" );
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document.write( "u + v = 32, (3)\r\n" );
document.write( "u - v = 20. (4)\r\n" );
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document.write( "To solve them, add equations (3) and (4) (both sides). You ill get\r\n" );
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document.write( "2u = 32 + 20, or 2u = 52. Hence, u =  = 26.\r\n" );
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document.write( "You just found the speed of the boat in still water. It is 26 mph.\r\n" );
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document.write( "Now from (3) v = 32 - u = 32 - 26 = 6.\r\n" );
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document.write( "Thus the current rate is 6 mph.\r\n" );
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document.write( "Answer. The speed of the boat in still water is 32 mph. The current rate is 6 mph.\r\n" );
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document.write( "For many other solved problems on upstream and downstream trips see the lessons \r
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document.write( " - Wind and Current problems \r
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document.write( " - More problems on upstream and downstream round trips \r
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document.write( " - Selected problems from the archive on the boat floating Upstream and Downstream \r
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document.write( "Read them attentively and learn how to solve this type of problems once and for all.\r
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document.write( "Also, you have this free of charge online textbook in ALGEBRA-I in this site\r
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document.write( " - ALGEBRA-I - YOUR ONLINE TEXTBOOK.\r
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